1. Field of the Invention
The present invention relates to a noble gas discharge lamp. More particularly, the present invention relates to a noble gas discharge lamp comprising a light emitting layer comprising an aperture inside a glass bulb, and a pair of outer electrodes in the shape of a belt outside the glass bulb; in which the light emitting layer is improved so as to increase the light output, and can produce a stable travel of electric discharge.
This application is based on patent applications Nos. Hei 9-72054 and Hei 9-72071 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
The applicant of the present invention previously proposed the noble gas discharge lamp shown in FIGS. 8 to 10. In FIGS. 8 to 10, reference number 1 indicates an airtight outer enclosure in the shape of a straight tube, and is comprised of as a glass bulb, for instance. On the inside of the outer enclosure 1, a light emitting layer 2 is formed which is comprised of one or more kinds of fluorescent substances, such as fluorescent rare earth substances, and fluorescent halorine acid salt substances. In particular, an aperture 2a having a certain opening angle is formed to extend over the full length of the light emitting layer 2.
The outer enclosure 1 is sealed by adhering glass plates in the shape of a disc to the ends of the glass bulb. However, for example, the outer enclosure 1 can also be sealed by tapering and cutting the ends of the glass bulb, while heating.
Moreover, the internal part of the outer enclosure 1 is filled with one kind of noble gas such as xenon (Xe), krypton (Kr), neon (Ne), helium (He), and the like, or a mixture thereof in which a metallic vapor such as mercury is not contained. Among these noble gases, noble gas comprising xenon as a main component is preferable.
An outer laminate 3 is rolled closely into the outside of the outer enclosure 1. The outer laminate 3 may be composed of a light transmitting sheet 4, a pair of outer electrodes 5 and 6, terminals 51 and 61, and an adhesive layer 9.
The light transmitting sheet 4 has a length equal to a length of the outer enclosure 1, and a thickness in a range of 20 to 100 microns. This light transmitting sheet 4 may be suitably comprised of polyethylene terephtalate (PET); however, polyester resin can be also used.
The above-mentioned pair of outer electrodes 5 and 6 are comprised of a metallic member having a light insulating property, the appearance thereof is tape shape, and it is adhered to one surface of the light transmitting sheet 4 so as to separate one outer electrode 5 from the other outer electrode 6 at a certain interval.
The terminals 51 and 61 are connected electrically to the ends of the outer electrodes 5 and 6. They are arranged at the edge of the light transmitting sheet 4 so that the ends thereof project from the edge of the light transmitting sheet 4. The thickness of the terminals 51 and 61 is preferably in a range of 0.1 to 0.5 mm.
The outer electrodes 5 and 6 and the terminals 51 and 61 are comprised of metals having differing corrosion potentials; for instance, aluminum foil in the shape of a tape is suitable for the outer electrodes 5 and 6. In addition to aluminum, nickel and other metals which have excellent electroconductivity and light insulating properties can comprise the outer electrodes 5 and 6. Regarding the terminals 51 and 61, copper in the shape of a strip is suitable. However, in addition to copper, metals such as silver, stainless steel, Cu-Ni alloy, and the like can comprise the terminals 51 and 61.
In particular, in the relationships of the widths between the outer electrodes 5 and 6 and the terminals 51 and 61, the width (w) of the outer electrodes 5 and 6, and the width (d) of the terminals 51 and 61 are preferably satisfied with the formula: 0.1 w.ltoreq.d.ltoreq.0.5 w.
The adhesive layer 9 has sticky properties and/or adhesive properties, and is adhered to one surface of the light transmitting sheet 4. The adhesive layer 9 is suitably comprised of a silicon adhesive agent; however, acryl resin adhesive agents and the like can also be used.
Moreover, plating layer (not shown in the Figures) is formed on terminals 51 and 61. The plating layer is comprised of metals which are different from metals comprising the outer electrodes 5 and 6 and the terminals 51 and 61, and which the corrosion potential difference is between the corrosion potential differences of the metals comprising the outer electrodes 5 and 6 and the terminals 51 and 61. For instance, in the case in which the outer electrodes 5 and 6 are comprised of aluminum foil, and the terminals 51 and 61 are comprised of copper, nickel, and lead-tin solder can be listed metals suitable for comprising the plating layer.
The plating layer can be formed preferably by electroplating or electroless plating; however, the plating layer can also be formed by an immersion or a flame spray.
The thickness of the plating layer is preferably in a range of 5 to 30 microns, more preferably in a range of 10 to 20 microns. However, a plating layer having a thickness outside the range can also be used.
The aforementioned outer laminate 3 is formed onto the outside of the outer enclosure 1 so that the outer electrodes 5 and 6 are positioned between the outer enclosure 1 and the light transmitting sheet 4. One edge 4a of the light transmitting sheet 4 is laminated and adhered to the other edge 4b at the following second opening portion 8. Moreover, a first opening portion 7 is positioned at one ends of the outer electrodes 5 and 6, and the second opening portion 8 is positioned at the other ends of outer electrodes 5 and 6. The light from the light emitting layer 2 is emitted mainly from the first opening portion 7 via the aperture 2a.
The noble gas discharge lamp comprising the above-mentioned components can be produced by the following steps.
A water soluble fluorescent paint is made by mixing water soluble fluorescent substances having an emission spectrum in a blue range, a green range, and a red range, for example. Next, the light emitting layer 2 is formed by coating a water soluble fluorescent paint on the inside of the outer enclosure 1 comprised of a glass bulb, by drying and then firing.
The aperture 2a is formed by peeling off and by forcibly removing a part of the light emitting layer 2, while maintaining a certain opening angle, by using a scraper (not shown in Figures). The obtained outer enclosure 1 is sealed and is filled with a certain amount of noble gas such as xenon and the like.
As shown in FIGS. 9 and 10, the outer laminate 3 is formed by positioning one pair of the outer electrodes 5 and 6 on the light transmitting sheet 4 so as to be disposed with a certain space therebetween, so that the terminals 51 and 61 project out from the edges of the outer electrodes 5 and 6, and by forming the adhesive layer 9 onto the upper surfaces of the light transmitting sheet 4 and the outer electrodes 5 and 6.
As shown in FIG. 11, the unfolding outer laminate 3 obtained by the above-mentioned steps is positioned on the stage 10. The outer enclosure 1 is positioned on the outer laminate 3 so that the outer enclosure 1 is positioned on the edge 4a of the light transmitting sheet 4, and the longitudinal axis of the outer enclosure 1 is parallel to the longitudinal axis of the outer electrodes 5 and 6. Rollers 11 and 11 are positioned so that the outer enclosure 1 is contacted with some pressure to the light transmitting sheet 4, while maintaining the above conditions.
While maintaining the above conditions, as shown in FIG. 11, the stage 10 is moved in the direction M, and is then moved in the direction N. Because of these movements, the outer laminate 3 is wound around the outside of the outer enclosure 1, and one edge 4a is piled on the other edge 4b of the light transmitting sheet 4, as shown in FIG. 8. Then, the noble gas discharge lamp is produced by adhering the edges 4a and 4b of the light transmitting sheet 4 with the adhesive layer 9.
The resulting noble gas discharge lamp is switched on to produce light by applying a high voltage of high frequency (for example, a frequency of 30 kHz and a voltage of 2500 V.sub.o-p) to the outer electrodes 5 and 6, from an inverter circuit 12, via the terminals 51 and 61. Light is emitted from the first opening portion 7 via the aperture 2a.
For instance, the voltage applied to the outer electrodes 5 and 6 is approximately 2500 V.sub.o-p in a noble gas discharge lamp of which the outer enclosure 1 is 8 mm in external diameter and 360 mm in total length.
In particular, mercury is not included in this noble gas discharge lamp; therefore, large amounts of light are generated instantaneously when the lamp is lit. That is, light increases to full quantity (approximately 100%) as soon as the lamp is lit. Moreover, light quantity and discharging voltage of the obtained noble gas discharge lamp are not influenced by the surrounding temperature. Therefore, when the noble gas discharge lamp is used in illumination scanning devices, for instance, the illumination intensity on a scanned document can be raised, and therefore, scanning precision of the scanned document can be improved.
Moreover, it is anticipated that the noble gas discharge lamp will have the following effects. The plating layer is formed between the outer electrodes 5 and 6 and the terminals 51 and 61; therefore, even if the outer electrodes 5 and 6 and the terminals 51 and 61 which are comprised of metals having different corrosion potential differences each other, are connected directly generation of corrosion due to the contact of different kinds of metal can be prevented.
In particular, when the width (w) of the outer electrodes 5 and 6 and the width (d) of the terminals 51 and 61 are set to satisfy the following formula: 0.1 w.ltoreq.d.ltoreq.0.5 w, corrosion due to contact of different kinds of metal can be prevented, in company with the existence of the plating layer. Therefore, stable travel of electric discharge of the noble gas discharge lamp can be maintained for long periods.
However, when the width (d) of the terminals 51 and 61 is less than 0.1 w, contact intensity to the outer electrodes 5 and 6 of the terminals 51 and 61 is decreased. In contrast, when the width (d) of the terminals 51 and 61 is more than 0.5 w, in winding the outer laminate 3 around the outside of the outer enclosure 1, the terminals 51 and 61 could not be wound around the outside of the outer enclosure 1 more easily. This process is extremely troublesome. Therefore, it is preferable that width (w) of the outer electrodes 5 and 6 and the width (d) of the terminals 51 and 61 satisfy the above-mentioned formula.
Moreover, the following effects can be obtained in the process for products. The adhesive layer 9 is formed on one surface of the light transmitting sheet 4; therefore, the outer laminate 3 can be adhered closely to the outside of the outer enclosure 1 by a simple step, that is, simply by rolling the outer enclosure 1 onto the outer laminate 3. In addition, the outer electrodes 5 and 6 are positioned previously so as to be disposed at a certain interval from each other on the light transmitting sheet 4; therefore, in adhering the outer laminate 3 to the outer enclosure 1, it is not necessary to adjust the positioning of the outer electrodes 5 and 6 to maintain a certain interval therebetween. Therefore, it can be anticipated that not only will the work efficiency be greatly improved, but automated production of the noble gas discharge lamp is also possible. That is, production of the noble gas discharge lamp in large quantities may be anticipated.
As described above, when the noble gas discharge lamp is used in a scanning device, the irradiance of the emitted light from the light emitting layer 2 can be high due to the existence of the aperture 2a. Therefore, the intensity of illumination on a document being scanned may be increased. As a result, accurate scanning of documents can be ensured.
However, in recent years, in order to manage a business with high efficiency, improvement in feeding speed of documents in office automation device is desired. At high speeds the scanning accuracy of documents (the resolution) tends to decrease.
In order to scan documents at high feeding speeds, it is preferable to increase the light output to increase the illumination intensity on the illuminated document. For example, the diameter of the outer enclosure 1 may be increased, and the electrical power input to the noble gas discharge lamp may be increased, easily increasing the light output. However, the interval between the surface of the illuminated document and this noble gas discharge lamp is narrower, such as 6 to 12 mm, in an illuminating device. Therefore, it is difficult to dispose the noble gas discharge lamp comprising an outer enclosure 1 having a larger diameter than that range.
When the electrical power to be input to the noble gas discharge lamp is increased without a change in size thereof, it is possible to increase the emitting light quantity in proportion to the increase of electrical power. However, the rate of increase in the light emitting quantity is small in proportion to the increase of input electrical power. It is therefore impossible to obtain an illumination intensity on an illuminated document sufficient to ensure full scanning accuracy.
Moreover, this noble gas discharge lamp is different from lamps having one discharge along the longitudinal direction of the outer enclosure 1, such as a noble gas discharge lamp having a hot cathode or a cold cathode. More specifically, innumerable discharges occur between the outer electrodes 5 and 6 (discharges are generated approximately perpendicularly to the longitudinal direction of the outer enclosure 1); therefore, when such a light is turned on, light is emitted in a striped pattern in the above-mentioned noble gas discharge lamp. Electric discharges in a striped pattern cannot be comfirmed under normal lighting conditions.
However, when the output electric power from the inverter circuit 12 is decreased 10%, for example, by a change of voltage from a power source, the electric discharges in a striped pattern can be confirmed. Moreover, the electric discharging positions (points) are not stable and travel in the longitudinal direction of the outer enclosure 1, without interruption. The light emitting from aperture 2a therefore becomes intermit. As a result, the illumination intensity on the illuminated document decreases.
In particular, in the case of employing the noble gas discharge lamp in the illumination device for the office equipment such as facsimile machines, image-scanners, and the like, the light intensities at the points in the longitudinal direction of the aperture 2a change continuously. Therefore, it is possible that the scan accuracy of the illuminated document is extremely degraded, and the quality of reproduction is also degraded.